Magnetic disk device

ABSTRACT

A magnetic disk device having a cover of a simple structure having high rigidity and not easily deformable by pressure from the outside. An envelop surface configuration ( 46 ) of at least a portion of a cover ( 40 ) positioned opposite a magnetic disk ( 2, 43 ) is made generally conical, such that the distance from the magnetic disk decreases along a direction from the vicinity of a rotating shaft of a motor, as the center, toward the outer periphery of the magnetic disk, thereby reducing the amount of deformation of the cover, particularly in the vicinity of the rotating shaft of the motor.

TECHNICAL FIELD

The present invention relates to a small magnetic disk device used in acomputer or the like.

BACKGROUND ART

A problem has recently arisen that, in magnetic disk devices mounted inmobile appliances such as notebook computers, it is necessary to make acover sufficiently rigid in the direction toward the magnetic disksurface. For example, in notebook computers and magnetic disk devicesincorporated in the notebook computers, the magnetic disk device isordinarily mounted under a palmrest portion closer to the computer frontside relative to the keyboard. In such a case, if the palmrest portionis strongly pressed by a person, the pressed portion is warped andpresses the cover of the magnetic disk device mounted under the palmrestportion incorporated mounted. The cover of the magnetic disk device isordinarily made a thin metal plate. At worst, a portion of the warpedcover is brought into contact with the magnetic disk rotating in themagnetic disk device. There is a demand for thinner mobile appliancesand thinner magnetic disk devices incorporated in the mobile appliances.Therefore, it is thought that this problem will become more serious.

In view of this problem, devices for improving the rigidity of covershave been provided. For example, a method is known in which areinforcing member of a high rigidity is placed in a space between amagnetic disk and a cover and is connected to the cover and to a base byusing fastening screws (see, for example, Japanese Patent Laid-Open No.2002-343071).

The shape of a conventional cover will be described with reference toFIGS. 6 to 8. FIG. 6 shows a magnetic disk device using a conventionalcover. FIG. 7 is a sectional view of the conventional cover. FIG. 8 is asectional view taken along a line passing through the rotating shaft ofa motor. As can be seen in FIG. 7, drawn portions 70 having asemicircular sectional shape are formed in a sectoral pattern above andopposite a magnetic disk to ensure the desired rigidity of the cover.

DISCLOSURE OF THE INVENTION

The conventional technique of placing a reinforcing member has drawbacksin that the cost is increased because of the need for the component partin addition to the cover and it is not suitable for a thin devicebecause it increases the thickness of the device.

To solve the above-described problem, the present invention provides amagnetic disk device including a magnetic disk, a motor for rotating themagnetic disk through its rotating shaft, a head for writing data to themagnetic disk or reading out data from the magnetic disk, an arm onwhich the head is supported, an actuator connected to the arm to movethe head generally in a radial direction across the magnetic disk, abase on which the magnetic disk, the motor and the actuator aresupported and accommodated, and a cover for enclosing the entire devicein association with the base,

wherein the cover is placed opposite to the magnetic disk and is formedso that the gap between the inner surface of the cover and the magneticdisk is reduced along a direction from the rotating shaft portion of themotor toward the outer periphery of the magnetic disk.

According to the present invention, a magnetic disk device having acover that has a simple structure and is not easily deformed under apressure from the outside can be provided.

According to the cover shape in accordance with the present invention,the static rigidity of the cover is improved to enable a pressure fromthe outside to be dispersed to the periphery, thereby reducing thestress and preventing deformation due to the stress. The cover shape canbe adapted for reduction in the thickness of a magnetic disk device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a magnetic disk device in the presentinvention;

FIG. 2 is a perspective view of the magnetic disk device in the presentinvention;

FIG. 3 is an exploded view of the magnetic disk device in the presentinvention;

FIG. 4 is a sectional view of the magnetic disk device in the presentinvention;

FIG. 5 is a perspective view of a cover in the present invention;

FIG. 6 is a perspective view of a magnetic disk device in an example ofthe conventional art;

FIG. 7 is a perspective view of a cover in the example of theconventional art;

FIG. 8 is a sectional view of the magnetic disk device in the example ofthe conventional art;

FIG. 9 is a plan view showing stress concentration in a cover inEmbodiment 1 of the present invention;

FIG. 10 is a plan view showing stress concentration in the cover in theexample of the conventional art;

FIG. 11 is a diagram showing the results of a simulation in the presentinvention and the example of the conventional art;

FIG. 12 is a perspective view of a cover in Embodiment 2 of the presentinvention;

FIG. 13 is a perspective view showing a section of the cover inEmbodiment 2 of the present invention;

FIG. 14 is a sectional view of a magnetic disk device in Embodiment 2 ofthe present invention;

FIG. 15 is a diagram showing the results of a simulation in the presentinvention and the example of the conventional art;

FIG. 16 is another sectional view of a magnetic disk device inEmbodiment 3 of the present invention; and

FIG. 17 is another sectional view of a magnetic disk device inEmbodiment 2 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Magnetic disk devices which represent embodiments of the presentinvention will be described in detail with reference to the drawings.

Embodiment 1

FIGS. 1 and 2 are perspective views of a magnetic disk device whichrepresents a first embodiment of the present invention. FIG. 3 is anexploded view of the magnetic disk device. FIG. 1 shows a state in whicha cover is opened. When the magnetic disk device is in operation, thecover is fixed to a base with seven screws. FIG. 2 shows a state inwhich the cover is removed. The magnetic disk device has the base 1, amagnetic disk 2 and an actuator 3. The magnetic disk 2 is driven androtated by a spindle motor 4. On one end of the actuator 3, a suspension5 is mounted and a head element is attached to an end portion of thesuspension 5. A magnet is fixed to a back surface of an upper yoke 7 andfixed on that base 1 with a predetermined spacing from a lower yoke 9maintained. A magnetic circuit is thereby formed. During operation, theactuator 3 is turned on a pivot shaft 6 by electromagnetic interactionbetween the magnetic circuit and an actuator coil 8 to position the headelement at a desired position on the magnetic disk 2. Reference numerals10 and 11 denote crush stops which are provided in correspondence withthe limits of the range of rotation of the actuator 3 to limit the rangeof rotation of the actuator 3, and which acts to reduce an impact forceat the time of collision. The crush stops 10 and 11 are formed ofelastic cylindrical members fixed on the base 1.

FIG. 4 is a sectional view along a line passing through a rotating shaft12 of the motor. Reference numerals 40 denote the cover, referencenumerals 43 the magnetic disk, and reference numerals 41 a clamp forfixing the magnetic disk 43 on a motor hub 45. An envelope surface 46 onthe external shape of the cover 40 is conical. When a force 44 to pressthe cover 40 is applied from the outside, the cover 40 is warped and agap 42 is reduced. As this gap 42, only a gap of about 0.5 mm isordinarily provided. Therefore, it is important to ensure certainrigidity of the cover. FIG. 5 is a perspective view showing a section ofthe cover.

A computer simulation based on a finite-element method was performed tocompare the rigidity of the cover in accordance with the presentinvention and the above-described conventional cover shown in FIGS. 6 to8.

The shape of the cover in the embodiment is a stepped conical shape, asshown in the sectional view of FIG. 4, the perspective view of FIG. 5and a plan view of FIG. 9. That is, referring to FIG. 9 showing a planview of the cover, concentric circles are formed around andconcentrically with a circle formed on the cover above a rotatingcentral portion from the rotating shaft 12 to the clamp 41. Thedifferences in height at the steps formed in the cover as between theconcentric circles are equal to each other. As indicated at 46 in FIG.4, the envelope surface on the external shape of the cover 40 isconical. This cover shape, in which the shape of the portion above therotating shaft 12 portion is flat and circular, is referred to as astepped conical shape.

FIG. 9 is a plan view of the cover in accordance with the presentinvention. FIG. 10 is a plan view of the conventional cover. Models ofthese covers were made by using a piece of finite element methodanalysis software and were divided into meshes for a shell element modelone side of which is about 2.0 mm. Holes for fastening with screws (90,91, 92, 93, 94, 95, and 96 in FIGS. 9, 100, 101, 102, 103, 104, 105, and106 in FIG. 10) were fixed under a perfect restraint condition and apressure of 10N was applied in the cover pressing direction to the coverat the position corresponding to the rotating shaft of the motor. Inactuality, a distributed load was applied to an area having a diameterof 23 mm about the rotating shaft of the motor such that the totalpressure was 10N (see 44 in FIGS. 4 and 80 in FIG. 8). The cover is madeof aluminum and has a thickness of 0.4 mm. The amount of warp underthese conditions was computed. FIG. 11 shows the results of computation.In each cover, the maximum warp was caused above the rotating shaft ofthe magnetic disk (97 in FIG. 9, 107 in FIG. 10). However, it can beunderstood that the static rigidity of the cover in accordance with thepresent invention is four times or more larger than that of theconventional cover. The main stress in the cover was examined to findthat the stress was distributed in a peripheral annular portion(blackened portion 98 in FIG. 9) in the cover of the present invention,while the stress was concentrated on a crossing portion (blackenedportion 108 in FIG. 10) in the conventional cover.

That is, it was found that the stress was concentrated on a low-rigidityportion. In the conventional cover, the rigidity of the crossing portionis low and the stress is concentrated on this portion. In the cover ofthe present invention, steps are formed by heightening the centralportion relative to the peripheral portion, so that the rigidity of thecentral portion is higher than that of the peripheral portion. Since thesteps are provided, the rigidity is reduced along a direction toward theperipheral portion to disperse the stress. Therefore, the amount ofdeformation of the cover is reduced.

That is, since stress is concentrated on a portion of a low rigidity,the stress is concentrated in the narrow crossing portion at the centerof the conventional cover to largely deform the cover. In the cover ofthe present invention, the rigidity is gradually reduced from thecentral portion to the peripheral portion, that is, the stress isdispersed to the peripheral portion, so that the maximum stress isreduced and the amount of deformation of the cover is also reduced.

In the results of the simulation, while the maximum stress value of theconventional cover was 3.7×10⁷ (N/m²) to 5×10⁷ (N/m²), the maximumstress value of the cover of the present invention was 2.5×10⁷ (N/m²) to2.7×10⁷ (N/m²). That is, it was found that in the cover of the presentinvention the applied pressure was adequately dispersed to limit themaximum stress to reduce the amount of warp.

That is, the steps are formed to enable the stress to be dispersed tothe stepped peripheral portion, thereby ensuring the desired rigidity.While an arrangement having four steps has been described as anembodiment of the present invention, it is possible to increase thenumber of steps to disperse stress to the periphery. Since it ispossible to enable stress to be dispersed to the peripheral side byproviding steps, the rigidity of the cover can be improved even if thenumber of steps is not four. If three or more steps are provided, acertain effect of dispersing pressure and reducing the maximum stresscan be obtained. However, it is preferable to provided four or moresteps.

In the plan view of the cover shown in FIG. 9, the cover is circular andformed around and concentrically with the circular portion formed abovethe rotating shaft central portion from the rotating shaft 12 to theclamp 41, and the differences in height at the steps formed between theconcentric circles are equal to each other, so that the envelop surface46 on the external shape of the cover 40 is conical. However, the sameeffect can be obtained even if the envelope surface 46 is not conical.That is, the same effect can be obtained even if the distances betweenthe concentric circles are not constant and the envelope surface 46 isnot conical.

Thus, a cover structure can be realized which is simple and easy tomanufacture, and in which the amount of warp of the cover in anout-of-plane direction, i.e., the direction toward the magnetic disksurface, is small since the rigidity is high and since a pressure fromthe outside is absorbed in the stepped portions.

That is, since a stress caused in the cover can be dispersed to reducethe warp of the cover, the worst event can be avoided in which, in acase where thickness of the magnetic disk device is reduced, a portionof the cover of the magnetic disk device cover is brought into contactwith a portion of the magnetic disk rotating in the magnetic disk devicewhen the cover is warped.

Also, because the material of the cover is a metal such as aluminum,stainless steel or an alloy of such metals for high rigidity againstpressure in the direction perpendicular to the cover surface, a coverstructure in which the amount of warp in the direction toward themagnetic disk surface can be realized by using a method such as pressingeasy to carry out.

Embodiment 2

The shape of a cover in another embodiment will be described withreference to FIGS. 12 to 14. FIG. 12 is a perspective view of the cover.FIG. 13 is a perspective view showing a section of the cover. FIG. 14 isa sectional view taken along a line passing through the rotating shaftof the motor. In Embodiment 1, only a portion of the envelope surface ofthe surface shape of the cover forms a conical shape, as indicated at 46in FIG. 4. In Embodiment 2, the surface shape of the cover directlyforms a conical shape. In actuality, the cover shape above the rotatingshaft 12 is a circular flat shape and the cover has the shape of atruncated cone. However, the shape of the cover in Embodiment 2 isreferred to as a conical shape in relation to Embodiment 1.

FIG. 15 shows the values of the characteristics of the cover inEmbodiment 2 computed by the finite-element method. The conditions forcomputation are the same as those in Embodiment 1 shown in FIG. 11. Asshown in FIG. 15, substantially the same characteristics as those shownin FIG. 11 were obtained. A case is conceivable in which a material usedfor the cover, the method of manufacturing the cover, or restrictions onthe sizes of component parts housed are such that directly forming thecover surface shape into a conical shape is more convenient than formingthe envelope surface on the cover surface shape into a conical shape. Insuch a case, Embodiment 2 is effective.

In Embodiment 2, the maximum warp in the same simulation based on thefinite-element method as that in Embodiment 1 was 0.14 mm above themagnetic disk rotating shaft and the maximum stress in the peripheralportion was 3.0×10⁷ (N/m²), which results are similar to those inEmbodiment 1. That is, the effect of improving the rigidity of the coverwas obtained in the case of forming into a conical shape.

That is, the stress was dispersed to the peripheral portion by makingthe cover shape conical, as in the case of Embodiment 1. Thus, therigidity of the cover can be increased.

It is also possible to increase the rigidity of the cover by making thecover surface shape domed.

Embodiment 3

FIG. 16 shows a case where the cover is formed into a stepped shape suchthat the envelope surface on the cover surface is formed into a domedshape (hereinafter referred to as “stepped dome”) different from aconical shape. FIG. 16 is a sectional view taken along a line passingthrough the rotating shaft of the motor. As indicated at 161 in FIG. 16,the stepped-dome shape is such that differences in height are providedin a stepping manner in the cover of the magnetic disk device and theenvelope surface on the cover surface shape has a domed shape.

The difference from Embodiment 1 resides in that the envelope surface161 on the cover surface shape for ensuring the desired rigidity has astepped-dome shape different from a conical shape. Also in this case, apressure applied to the cover is adequately dispersed to limit themaximum stress and reduce the amount of warp. A case is conceivable inwhich a material used for the cover, the method of manufacturing thecover, or restrictions on the sizes of component parts housed are suchthat forming the envelope surface of the cover surface shape into astepped-dome shape is more convenient than forming the envelope surfaceon the cover surface shape into a conical shape.

Further, the stepped-dome cover surface shape may be replaced with asmoothly domed shape to ensure the desired rigidity. FIG. 17 shows acase where the cover surface face shape is a domed shape. FIG. 17 is asectional view taken along a line passing through the rotating shaft ofthe motor. As indicated at 171 in FIG. 17, the surface shape of thecover of the magnetic disk device is formed into a domed shape to enablean applied pressure to be adequately dispersed, thereby limiting themaximum stress and reducing the amount of warp. A case is conceivable inwhich a material used for the cover, the method of manufacturing thecover, or restrictions on the sizes of component parts housed are suchthat directly forming the cover surface shape into a domed shape is moreconvenient than forming the envelope surface on the cover surface into adomed shape.

Thus, a cover shape structure enabling stress to be dispersed to theperiphery is adopted to reduce the amount of deformation of the cover.

Also, because the material of the cover is a metal such as aluminum,stainless steel or an alloy of such metals for high rigidity againstpressure in the direction perpendicular to the cover surface, a coverstructure in which the amount of warp in the direction toward themagnetic disk surface can be realized by using a method such as pressingeasy to carry out.

1. A magnetic disk device comprising a magnetic disk, a motor (4) forrotating the magnetic disk through its rotating shaft (12), a head forwriting data to the magnetic disk or reading out data from the magneticdisk, an arm on which the head is supported, an actuator (3) connectedto the arm to move the head generally in a radial direction across themagnetic disk, a base (1) on which the magnetic disk, the motor (4) andthe actuator (3) are supported and accommodated, and a cover (40) forenclosing the entire device in association with the base (1), whereinthe cover (40) is placed opposite to the magnetic disk and is formed sothat the gap between the inner surface of the cover (40) and themagnetic disk is reduced along a direction from the rotating shaftportion of the motor (4) toward the outer periphery of the magneticdisk.
 2. A magnetic disk device comprising a magnetic disk, a motor (4)for rotating the magnetic disk through its rotating shaft (12), a headfor writing data to the magnetic disk or reading out data from themagnetic disk, an arm on which the head is supported, an actuator (3)connected to the arm to move the head generally in a radial directionacross the magnetic disk, a base (1) on which the magnetic disk, themotor (4) and the actuator (3) are supported and accommodated, and acover (40) for enclosing the entire device in association with the base(1), wherein the cover (40) is placed opposite to the magnetic disk andis formed into a circular stepped-dome shape with a difference in heightsuch that the gap between the inner surface of the cover (40) and themagnetic disk is reduced step by step along a direction from therotating shaft portion of the motor (4) toward the outer periphery ofthe magnetic disk.
 3. The magnetic disk device according to claim 2,wherein the circular stopped-dome shape portion of the cover (40) isformed in a portion facing the magnetic disk.
 4. A magnetic disk devicecomprising a magnetic disk, a motor (4) for rotating the magnetic diskthrough its rotating shaft (12), a head for writing data to the magneticdisk or reading out data from the magnetic disk, an arm on which thehead is supported, an actuator (3) connected to the arm to move the headgenerally in a radial direction across the magnetic disk, a base (1) onwhich the magnetic disk, the motor (4) and the actuator (3) aresupported and accommodated, and a cover (40) for enclosing the entiredevice in association with the base (1), wherein the cover (40) isplaced opposite to the magnetic disk and is formed into a steppedconical shape such that the gap between the inner surface of the cover(40) and the magnetic disk is reduced so as to have equal differences inheight along a direction from the rotating shaft portion of the motor(4) toward the outer periphery of the magnetic disk.
 5. The magneticdisk device according to claim 4, wherein the stopped conical shapeportion is formed in a portion of the cover (40) facing the magneticdisk.
 6. A magnetic disk device comprising a magnetic disk, a motor (4)for rotating the magnetic disk through its rotating shaft (12), a headfor writing data to the magnetic disk or reading out data from themagnetic disk, an arm on which the head is supported, an actuator (3)connected to the arm to move the head generally in a radial directionacross the magnetic disk, a base (1) on which the magnetic disk, themotor (4) and the actuator (3) are supported and accommodated, and acover (40) for enclosing the entire device in association with the base(1), wherein the cover (40) is placed opposite to the magnetic disk andis formed into a circular domed shape such that the gap between theinner surface of the cover (40) and the magnetic disk is reduced along adirection from the rotating shaft portion (12) of the motor (4) towardthe outer periphery of the magnetic disk.
 7. The magnetic disk deviceaccording to claim 6, wherein the circular domed shape portion is formedin a portion of the cover (40) facing the magnetic disk (2).
 8. Themagnetic disk device according to claim 1, wherein the material of thecover (40) is a metal such as aluminum, stainless steel or an alloy ofsuch metals for high rigidity against pressure in a directionperpendicular to the cover (40).
 9. The magnetic disk device accordingto claim 1, wherein the cover shape of the cover (40) above the rotatingshaft portion (12) of the motor (4) is a circular flat shape.